Communication with moving trains



March 22g-'1933. H, A. AFFEL ET AL 1,902,817

COMMUNICATION WITH MOVING TRAINS Filed oct. 2, 1929 2 sh'ts-'shgxlfl LFixed stamm ATTORN EY March 28, 1933. H. A. AFFEL.` Er A1. 1,902,817

COMMUNICATION. WITH MOVING TRAINS Filed oct. 2, 1929 2 sneetssheet 2 6 71 T l Mij-i] 15P;

Fzxed Statc'on/ ml Z-IL ATTORN EY Patented Mar. 28, 1933 UNITED STATESPATENT. ori-ICE HERMAN A. AEEEnoE EIDGEWoon, AND ESTILI. I. GEEEYN,v-orEAST ORANGE, NEW JERSEY, AssIGNoRs To AMERICAN TELEPHONE AND TELEeRAPHCOMPANY, A

CORPORATION OF NEW YORK coMMUNIoATIoN WITH MOVING TRAINS Application meamember` 2, 192e.` seriai Nofaeasa.

for communicating-with vehicles in motion,

such, for example, as moving railway trains. One purpose of theinvention is to make it possibleto communicate simultaneously with aconsiderable number of trains on the same track and to do so with theminimum amount of apparatus and .with a minimum use of the frequencyspectrum. Another purpose of the invention is to increase thereliability* of such communication. Still another purpose is tov makethe maintenance of the transmission equivalent's between the landstation and the train automatic and not requiring the special attentionof an operator either on the train or the land station.

Briefly, the invention consists in using the existing communicationlines,l such as telephone or telegraph' lines, or other circuits whichextend along therailway,and connect-V ing with the moving train byinductive or capacitive coupling across the air gap. The communicationline is divided electrically into separatesections of suitable lengthsand fixed stations, each transmitting in twodif rections. The signalingis effected by means of a carrier frequency in order to afford bettercoupling between the vehicles and the line, and preferably one pair offrequency bands is assigned to each train. The same frequency bands maybe employed for trains which do not run simultaneously in the samesection.

. By locating the division between two sections at appropriate places,such as importantcities, it becomes a relatively simple matter toprovide telephone connections between a train and any subscribersstation in an expansive telephone system. This meansa two-wiretermination at the land station but on the trainit would be feasible toprovide a four-wire sub-set termination, this being possible in view ofthe limitedv number of vsub-sets involved.

' in connection with the accompanying drawings, in which Figure l showsthe manner in which a railroad route might be divided into sections;Figs. 2 and 3 show the manner in which a plurality of telephone ortelegraph lines along the right of way may be associated in groups forthe transmission of signals;

Fig. 4 shows one specific arrangement for transmission between a movingtrain and the parallel line, `making use of combined loop and antenna;Fig. 5 shows in greater detail the arrangement of basic apparatus atafiXed station and a cooperating train station; Fig. 6 is amodilicationof Fig. 5;-Fig. 7 shows provision for compensatingfordistance of thetrain from a fixed station; and Fig. 8 gives a schedulearrangement of communica@ tion witha large number of trains 4on the sametrack with a minimum use of apparatus and frequencyspectrum. Y

- The method of transmission which we have. n. found most suitable forsuch communication is to transmit at carrier frequencieszover thetelephone line lparalleling the track and to use inductive or capacitivecoupling for the connection to the train.,` Such an arrangenient' isindicated in Fig. l in which the line along the track is electricallydivided into Separatesections a, b, cof reasonable length, say of about200 miles, it being of course desirablethat the various sections shallbe of about the same length, although'no severe restrictions in thisdirection arenecessary. AtA orinear the center of each of these sectionsthere is 'located a fixed station, such as A, B, C,- adaptedto'communicate with trains in that section but 4with, no other trains."This 'station A' would provide communication in the section betweenpointsuD and E,station B between points E and F, and station C betweenpoints .F and Gr. It will be `noted i that this arrangement does `notprovide'any-'- y repeaters 'along'the sections but instead of this thesections are made sufficiently short" so that any fixed station. I iiaycommunicate directly in both directionsiwith trains in that section.This. evidently covers the :distance with a minimum amount of apparatus,and

circuit arrangementl since it provides at'all times a carrier circuit tothe neares'tvfcity along the route and rfrom this point voice.

ka5 we consider this. an important featureof our'` invention. It alsoVfurnishes a, convenient 50, be desirablel touse a combined loop andancircuits can be built up to distant subscribers stations withoutdifficulty.

In order to avoid confusion during the period when the train isapproximately equidistant from two terminals, it may be desir.-

able that the transmitting and receiving fre'- quenciesl be inverted atalternate stations. l

There are a number of ways in which the telephone lines may beassociated or used for the presentl signaling purposes but there are twowhich we nd particularly advantageous. In the one we transmit betweentwo separated wires or groups of wires, and inthe second we transmitover a wire or group of wires with ground return. Fig. 2 shows the firstVof these methods. In this figure it will be seen that the wires l, 2, 3and 4 are adapted for -ordinary telephonie purposes, .being associatedfurther for phantom operation. The same is true of the group of wires 21to 24. yFor the purpose of the high frequency V signaling now proposedthehigh frequency Vcurrent maybe sent from either the Xed or the moving.station over a metallic circuit, one side of this .metallic circuitcomprising the lines l to 4 and the other side comprising the wires 2lto 24. 'Suitable high pass and low pass filters are shown in thefigures, and by means of these, proper separation is maintained betweenthe high frequency and the low frequency signal channels.

In Fig.r3 a group of wires 31Yto 34 isused as one side of the highfrequency circuit and the ground is used for return. Again suitable highpass and low'pass filters are provided to maintain separation betweenthe different signaling channels.

v In order that the message shall not be picked up unnecessarily byother telephone or telegraph lines adjacent to those which are beingused, it may be desirable to introduce into these additional linessuitable loading or choke coils which will prohibit the flow of the highfrequency signals. l

As stated above, we employ some form Aof inductive or capacitivecoupling with the train. We have found that approximately the sametransmission loss is involved with either form of coupling and itmaytherefore tenna, thatV is, to use the inductanceof a loop for thetransmittercoupling and its capacityto ground for the receivingcoupling, or

the reverse. Such an arrangement is shown Y in Fig. 4, inwhichtransmission from the 1train takes place vover a loop, that is, byinductive coupling, whereas reception takes place over the loopconsidered as an antenna,

lthat is,by capacitive coupling.l This mode of yoperation .has anadvantage in that it.

greatly reduces the transmission loss which would otherwise berequiredin the receiving filterto discriminate against the transmittingfrequency range.

i kA more detailed drawing of the arrangement of apparatus at the fiXedstation and the train station is shown in Fig. 5. The" line L isconnected with any remote subscribers station, and by means of thehybrid coil II is adapted in the well known manner for two-waycommunication. Incoming low frequency signals over the line L are usedto modulate a carrier frequency f2 and, on suit- Y For signaling in thereverse direction the microphone currents at the train station -areimpressed upon la modulator supplied with'v carrier frequency f1 andafter transmission through suitable protecting filters and amplifiers isimpressed on the loop 4. The signals being picked up by the line 3 arethen amplified and impressed on a demodulator supplied with a carrierfrequencyv f1 and theV demodulated product is then transmitted overthe.line L. v

As the train travels along there will be large and often verysudden-changes in trans-A mission dueto the following causes :v

(l) Changes in separation v,between the train and the paralleling line.

(2) Changes ina vertical direction in the position of the couplingtdevice withy refers.

ence to the line. .A f l f (3) The presence of another train vbetweenthe coupling device and the line.Vv

(4) Varying distance from the fixed station. Some of these variationsmay be eliminated or reduced by using two collectingv sources on' thetrain, one at the front yand one at the rear. This is especially helpfulin the case of thershort departures of the line from the track'such aswhen the line enters a dispatchers station. In any event, however, wefind it important that a pilot channel shall be provided tor stabilize'the transmission. Fig. G showsa fixed anda moving station with aschematic pilot channel for the purvpose described. In this figure thereis shown a twoewire termination for the land station, the hybrid coil Hmakingit possible to carry on two-way signaling with a remotesubscribers station. The low frequency incoming Asignal is modulatedagainst alocally generated high frequency carrier, the modulated signalthen being amplified at the transmitter-amplifier 6 and impressed on thetransmission line through the: high pass filter 7.

Modulatedhigh frequencyssignals coming amplifier 9, thereafter beingdemodulated and impressed on the line L. A Vprecisely similar equipmentis provided on the train station.

In order to obtain transmission level con-` trol we provide a pilotchannel consisting of a carrier frequency transmitted from the onestation to the other and preferably of a frequency near but not in thesignaling band. fo' In F ig. 6 there is shownat the train station at apilot control transmitter consist-ing of means for impressing on thelinethe pilot signal. This signal is picked up at the fixed station andtransmitted throughsuitable fil- 1*5 ters and a detector-amplifier 11,the output ofthis amplifier being used to control the gain in theamplifiers 6 and 9 by any suitable means. While this pilot 'signal hasbeen shown as being transmitted from the train 2o station, it is obviousthat it might be transmitted inthe reverse direction but we'iind itVpreferable to have most of the apparatus .for the pilot channel locatedat the fixed station ,n since itis desirable to have as little apparatusas possible on the train, and it is thus described in the figure. Itshould be pointed out, however, that with several fixed stations it maybe more advantageous to locate the Y `pilot channel receiving apparatuson the ltrain. We do not here describe the operation of the pilotchannel control in detail, any appropriate apparatus being permissiblesuch, for example, `as that described in pat- Vent to Clark, No.1,438,219, of December 12, 351922. However, because of the speed of thetrain the pilot channel should have almost instantaneous response tolarge transmission changes and `this we find can best be obtained Abyvarying either the B battery on the am- 4oplifier tubes or the gridvoltage on the modulator tubes, or both. This may be accoma' plished inany well known manner, such, for instance, as by adding to theregulation batp tery supply a variable positive potential ap- --plied tothe grid or a varying negative potential applied to the plate, thesepotentials varying directly with the rectified current received on thepilot channel. Such methods vof control are described in patents toAffel, 1,511,015, of October 7, 1924, or 1,574,780, of

March 2, 1926.

The pilot channel arrangements thus described are intended primarily to.take care of the variations coming Aunder items 1, 2

and 3 of page 6. It mightalso be used for taking care of the variationscoming under item 4; that is, the changes dueto varying distance betweenthe train and a fixed station, which changes will occur gradually. Sinceit may be difi'icult to take care of all variations with the pilotchannel, it will be desirable to relieve the pilot channel as much asfeasi-v ble and to this end we nd that the varia tion in transmissionlevel due to varying distance between the train and the fixed stationmay be compensated by an arrangement simi'-l lar to that shown in Fig.l7. 4This arranger;

ment provides, on the train, transmitting and receiving potentiometers18 and 19 whichare mechanically connected to a device which in turn isgeared to the wheels. This device is;

arranged to make contact at various intervals along the route and-thusmove the potentiometers up orfdownone step according to whether thetrain is leaving or :approaching the fixed station. The points 1, 2 and301il the path of the vehicle are so spaced that the distance betweenpoints equals the total span covered by a single station divided lbythe` total number of potentiometerV steps;` A switch or other device setat the beginning of the trip will arrange it so that the gain isincreased or decreased as desired. Obviously, many variations on this.may be conceived, for example, instead ofV being operated on aimileagerbasis yby virtue of being geared to the wheels, thepotentiometervcontrol might be operated by fixed devices set at suitablepoints along the road bed, these taking the 'Y i form of projectingarms, third rails, or vother special arrangements. i

.'The system as described may be operated y with a single carrierfrequency for both transmission and reception or with two differentcarrier frequencies f1 and f2', one for transmission and the other forreception. The second method has the advantage of moredefiniteseparation of thetransmitted and the received signals,`withcorresponding simplification of the terminal apparatus, but it usestwice as much of the frequency spectrum. j Thus far the description ofour invention With a `plurality of trains. One method which wecontemplate is that of providing a number of differentcommunicationchannels and arranging for each train to selectan idle channel. Theprocedure would be analogous to that in general telephone practice wherea group of circuits is` provided between two cities, from which theoperator selects an idle circuit.' In our system, for example, if coni'-munication were desired wit-h twenty trains,

The system thus far described ico .116 ods are available for suchcommunication iis" it wouldbe necessary to establish four or fivecommunication channels. It is evident, how` ever, that this arrangementrequires elabo-l rate and expensive equipmentv on each train in order tomake it possible to select any one of the available channels. ForVexample, the equipment needed for ringing individual trains we findbecomes rather complicated. A second method which We contemplate for ourinvention, and which provides'for better economy and simplicity, wouldmake use of a different pair of frequencies for each train. Vrlhismethod is practicable for 5 a small number of trains, but as-the totalnumber of trains on a given line is increased, the problem yof findingsuitable frequency bands ysulliciently separated in that portion of thefrequency spectrum where the attenur4 ation would not be excessive,becomes diiiicult. Further1nore,the apparatus at the fixed stationsywould become complicated ifeach of them is equipped to signal on solarge a number of carrier frequencies. y A .third and preferred methodwhich we 'ind'especially well adapted for the case-of a large number oftrains is to assign each train one, and only one, pair of frequencies,butto use the same pair of frequencies for several different trains. Itwill be clear that any two trains which do not runsimultaneously in thesame line section `can use the same pair of frequencies Without mutualinfterference.v Hence, the total number of pairs `of frequenciesnecessary in any line section "is equal to the maximum number of trainsrunning simultaneously in that section at a given time, and theassignment of frequencies to the. dierent trains then becomes a 80relatively simple matter. f

' y Consider, for example, the illustration in Fig. 8. This represents adiagram of the ruiming schedule for a theoretical railroad line coveringa distance of 600 miles between Y two cities A and B. Let us assume that-twelve trains a day are run in each direction between these two towns,the trains leaving the terminals on the even hours. The running timeforeach train is taken as twelvehours.

40 The schedule is drawn by plotting distances traveled as abscissae,and times as ordinates. In the diagram, the twenty-four hour period isassumed to be divided into a period from 8:00 A. M. to midnight duringwhich communic'ation is provided, and the periodV from midnight to 8 :00A. M. during which.V communication is unnecessary. The exact length ofthis period is, of course, immaterial. total distance of 600 miles isdivided into Y .six sections of 100 miles each, and it is as- Vsumedthat each of the fixed stations located at C, D and Ewill maintaincommunication for 100 miles on either side.

In this simple. illustration none fof the trains going from A to B runssimultaneously Nin the same section with the preceding or the followingtrain. Hence, all the twelve trains in the A-B direction can use thesame pair of frequencies f1 and f2. Similarly, all of the trains runningin the B-A direction may use a common pair 'of frequencies, but sincethese vtrains run simultaneously in the Y same section with trains goingin the A-B direction, this must be a new pair of frequencies f3 and f4.At each of the lixed sta- The channel at, all times and the apparatusatV the fixed stations used with maximum etliciency. lt may be noted incomparison that the second method proposed above would re-.

quire a total of fortyeight different frequency bands. y

lf the total number of trains in the assumed system were double-d, onetrain leaving each terminal every hour, then successive trainsV in eachdirection would Vrun simultaneously in the same line section. ln thisevent it would be necessary to use Yadierent pair'of frequency bands foralternate trains, and the total number of pairs ofbands required wouldbe eight instead of four. As an alternate solution of thislast situationit is evidentthat the fixed stations, could be placed closer together inorder tov avoid the contingency of two trains, with which communicationis to be maintained, being in the same section. I

lnV general, the procedure would be to set up a diagrammatic schedule ofthe type illustrated in Fig. 8 and from this determine for eachdirection of travel the trains which run simultaneously in any onesection. The proper assignment of frequencies for one direction thenbecomes obvious. A certain factor of safety may be required because thetrains cannot always run on schedule,but this means only the addition ofa small number of frequency hands or a reduction'in the length of thesections. Y y o Whilethisrsystem of communication has been describedY ina certain specific manner, it

- is t-o be understood that the scope of the invention covers manyVvariations therefrom.

,F or example, while it has beenrspecilica-lly stated that a pair offrequency bands is preferred for eachtrain', one for transmission andone for reception, it is to be understood that such twoeway signalingmay be maintained on one frequency band. Also, while in Fig. 8 thetrains are indicated as running lthrough the length ofthe railway linewith uniform speed, such will frequently notbe the case, and a correctdiagram for any train would show a slope of the line which changes fromone portion to'anotherinaccordanceV with the speed fof the train overagiven portion of the line.

What is claimed is:

l. ln a signaling systemto and from moving trains, a transmission linealong the route of the trains, means-for electrically dividingV saidline into a plurality of sectionsa fixed carrier frequency signalingstation near theV middle of each section and associated for twowaysignaling with the transmission line, and a plurality of trains eachprovided with inductive lmeans, for two-way signaling with ico movingtrains, a transmission line along the said line, eachV train a sectionbeing provided for' signaling on a different pair of carrier frequenciesand each fixed station being equipped for signaling simultaneously onthe pairs of carrier frequencies associated With the plurality oftrains.

2. In a system for signaling to and from ni'oving trains, a transmissionline along the route of the trains for transmitting signal current,means for electrically dividing said line into a plurality of sections,a fixed ca rrier frequency signaling station near the-middle of-eachsection and associated for tvvo-Way signaling With the transmission lineon a plurality of carrier frequencies, means thereat for modulating thecarrier frequency With the signal current and aV plurality of trainsvprovided with means for two-Way signaling with said line, means at eachfixed station .to provide a separate pair of carrier transmissionfrequencies for each train Which may simultaneously be in its section. Y

3. In a system for signaling to and from moving trains, a transmissionline along the route of the trains, means for electrically dividing saidline into a plurality of sections, a fixed carrier frequency signalingstation near the middle of each section and associated for two-Waysignaling with the transmission line, a train provided With means fortwo-Way signaling with said line, and means for controlling thetransmission level of the signals in accordance With the distance to thefixed station and in accordance with variations in the coupling betweenthe train and the transmission line.

4. In a system for signaling to and from moving trains, a transmissionline along the route of the trains, means for electrically dividing saidline into aplurality of sections, a fixed carrier frequency signalingstation near the middle of each section and associated for two-Waysignaling with the transmission line, a train provided with inductivemeans for two-Way signaling with said line, a pilot signaling channelfor indicating the transmission level of the communication circuit,

and means responsive to said indications for controlling the gain.

5. In a system for signaling to and from moving trains, a transmissionline along the route of the trains, means for electrically dividing saidline into a plurality of sections,

. a fixed carrier frequency signaling station near the middle of eachsection and associated for two-Way signaling With the transmission line,a train provided With inductive means for two-Way signaling with saidline, and means at the train for controlling the gain in accordance Withthe distance to the fixed station and means at the latter to control thegain in accordance With the variations in coupling.

6. In a system for signaling to and from route of the trains,meansforelectrically di-` viding said line into a plurality of sections,a fixed carrier` frequency signaling station near the middle of eachsection and associated for two-Way signaling with the transmission line,a train provided with inductive means for two-Way signaling With saidline, a pilot signaling channel for indicating-the trans-l mission levelof the communication circuit, means at the fixed station to control'thetransmission gain. in accordance With the variations in coupling, andfurther means at `the train for controlling the gain in accordance withthe distance to the fixed station.

7. In a system forsignaling to and from moving trains, a fixed signalingstation at one point along the route adapted fortwo-` route of thetrains, a fixed Vsignaling station at one pointalong said route adaptedfor;

tWo-vvay signaling with the transmission line, a trani provided withmeans for two-Way signaling with said line, a pilot signaling channelfor indicating the transmission levell 0f the communication circuit, andmeans responsive to said indications for controlling the gain of saidcommunication circuiti.,

9..In a system for signaling to and from moving trains, a section, oftransmission line along the route of the train, a fixed carrierfrequency signaling station near the middle thereof and associated withthe transmission line for signaling,'a` train provided with means forsignaling with said line, and means for controlling the transmissionlevel of the signals in accordance With the distance to the fixedstation and in accordance with variaifo,

` 9o l from ,moving trains, a transmission line along the tions in thecoupling between the train and the transmission line.

10. In a signaling system to and from movingl vehicles and comprising atransmission line along the route of vehicles, the line beingelectrically divided into a plurality of sections, 'a fixed carrierfrequency signaling` quencies one for incoming and one for out? goingsignals, means for adjusting the carrier frequency so that each train inany one section operates on a pair of carrier `frequencies differentfrom that forthe other trains in that section, the trains in anyl othersection being adapted to use the'sanie 'sets of carrier frequencies asin the first named section.

11. In a signaling system to and from moving vehicles and comprisingatransmission-line along the route of vehicles, the line beingelectricallydivided into a plurality of sections, a'iixed carrierfrequency signaling station near the middle of each section andassociated for two-way signaling with the transmission line andinductively coupled to the vehicles, carrier frequency transmitting andreceiving appara-tus on each train, each train operating on a pair o-fcarrier frequencies one for incoming and one for outgoing signals, meansfor adjusting the carrier frequency so that each train in any onesection `operates on a pair of carrier frequencies different from thatforV the other trains lin that section, the same pairs of carrierfrequencies being used on all sections and each section beingelectrically isolated from the other sections for carrier frequencysignals. 12. In a system of signaling toand from moving trainscomprising a transmission line along the route of the trains for audiofrequency signaling between widely separated points and fixed signalingstations along the line, thev method of signaling which consists insending the audio frequency message along the transmission line to thefixed station nearest the train, converting the message to a `modulatedcarrier wave, impressing this carrier wave on the transmission line,receiving the message inductively` on the train, and converting it tonormal audio frequency.

13. In a signaling: system to and` from moving Vehicles, a transmissionline along t the route of the vehicles, means for electricallydividingsaid line into a plurality of sections for frequencies above theaudiofrequency-range, a ixed carrier frequency signalingstation near'themiddle of each sec-V tion, means for two-way transmission ofr audiofrequency messages on said transmis sion line between any fixed stationand a remote point, means at any one of thel fixed stations forconverting the message to a carrier frequency wave and for impressingthe wave on the section of the transmission line adjacent the fixedstation for reception by a train in that section. f

14;. In a signaling system to and from moving vehicles, a transmissionline along the route of the Vehicles, means for electricallydividingsaid line into aplurality of sections for frequencies above thevaudio-frequency range, a fixed carrier frequency signaling station nearthe middle of each section, means sof for two way transmission of audiofrequency messages onsaid transmission line between any fixed stationand a remote point, means at any one of the fixed stations forconverting the message to acarrier frequency wave and for impressing thewave on the section -of the transmission line adjacent the xed stationtrolled automatically by the rota-tion of thev train wheels to adjustthe gain in accordance with the distance from. the nearest fixedstation. i

In testimony whereof, we have signed our names to this specificationthis 27th day of September, 1929. Y

HERMAN Y A. j AFFEL. ESTILL I. GREEN.

